1. Field of the Invention
The present invention relates to a method of interconnection routing for semiconductor chips, and more particularly to a method for preventing crosstalk by routing and evaluating the degree of crosstalk simultaneously.
2. Description of the Related Art
The connection path between components in a semiconductor integrated circuit has decreased with increased component quantity. Coupling between routing wires, known as crosstalk, can cause functional failures and timing degradation in a semiconductor integrated circuit. Crosstalk is more severe in deep sub-micron technologies, where neighboring wire coupling capacitance dominates the total net capacitance. Increased clock speed and reduced voltage supply in modern designs further worsen the problem.
Traditionally, to determine if a chip implementation will suffer from crosstalk, a circuit simulation is performed or a static analysis tool is run after placement and routing. If a problem is discovered, the nets are manually repaired to alleviate the crosstalk. In modern high density chip design, however, there may be numerous coupling issues found after the first placement and routing. The manual repair process is difficult and time-consuming. Additionally, repair of some nets may cause other nets to develop problems. In a worst-case scenario, there may be insufficient routing resources left to address all the issues.
The most efficient method of eliminating crosstalk in deep sub-micron chip design is to prevent problems during chip implementation, and omit testing after implementation. Thus eliminating post-route repairs to nets suspected of having crosstalk. There are various techniques such as cell sizing or buffer-insertion during placement to alleviate crosstalk. The effect, however, is limited due to lack of coupling data during the placement stage. Addressing crosstalk issues in the routing stage offers the best results, as all the data required for estimating coupling effects is available.
Several similar solutions were introduced in U.S. Pat. No. 5,883,812, one of which is to determine distance and coupling length between nets, yielding an approximate result. The method provided in U.S. Pat. No. 5,883,812, comprises the following steps. First a long connection path is installed in the middle of a connection channel. Another path is then installed around the connection channel, so as to reduce the number of cross points between the paths. This method, however, is unable to ensure the prevention of crosstalk.
A solution introduced in U.S. Pat. No. 5,972,41 is similar to the methods in U.S. Pat. No. 5,883,812, wherein problematic nets are placed first to ensure their safety, other nets are then placed normally. This method is equally incapable of guaranteeing that crosstalk will not occur.
An object of the present invention is to provide a method for preventing crosstalk by routing and evaluating simultaneously.
The present invention provides a method for a routing tool to prevent crosstalk in general nets utilizing a pre-determined noise database. The noise metrics are evaluated with respect to four modeling parameters, which are aggressor signal transition time, victim holding resistance, victim net total length, and coupled wire length. All four parameters can be quickly obtained during routing. To evaluate noise metrics during routing, a routing tool is not required to perform additional complex calculations; instead, existing data and simple geometric parameters are enough.
The method of the invention comprises the following steps. Providing an aggressor connection path as a first net. Providing a victim connection path according to the requirement of a second net. Determining a voltage ramp time of the aggressor connection path, a victim total length of the victim connection path, a coupled wire length between the aggressor connection path and the victim connection paths, and an equivalent load corresponding to the victim connection path. Evaluating noise metrics according to the voltage ramp time, the victim total length, the coupled wire length and the equivalent load. Modifying the victim connection path to shorten the coupled wire length if the noise metric is greater than a pre-determined value. Finally designating the victim connection path as the second net if the noise metric is less than the pre-determined value.
A further object of the present invention is to provide a coupling noise database, comprising several noise metrics, wherein each noise metric corresponds to a pre-determined set of parameters comprising a voltage ramp time of a aggressor connection path, a total length of a victim connection path, a coupled wire length between the aggressor connection path and the victim connection path, and an equivalent load corresponding to the victim connection path.
An advantage of the present invention is to accurately and simultaneously evaluate a noise metric between a victim connection path and an aggressor connection path while placing the victim connection path. Thus addressing crosstalk by preventing overflow of the noise metric.
A further advantage of the present invention is that the noise metric can be rapidly obtained. The noise metric of the next connection path can be determined quickly by effective information comparison, as nearly all parameters and corresponding noise metrics are recorded in a coupling noise database. Thus the total routing time is substantially reduced.
The following detailed description is given by way of example and not intended to limit the invention solely to the embodiments described herein.